Sunlight harvesting transparent windows

ABSTRACT

A photovoltaic system is formed as a window that is constructed of at least one polymer layer that is filled or decorated with metal nanoparticles and a window frame that includes one or more photovoltaic cells. The metal nanoparticles have a shape and size such that they display surface plasmon resonance frequencies in the near-infrared and/or the near-ultraviolet. The near-infrared and/or the near-ultraviolet radiations are scattered such that they are transmitted parallel to the face of the window to the photovoltaic cells, where an electrical current is generated.

CROSS-REFERENCE TO A RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser. No. 62/132,771, filed Mar. 13, 2015, the disclosure of which is hereby incorporated by reference in its entirety, including all figures, tables and drawings.

BACKGROUND OF INVENTION

A solar panel that allows light to pass through a pane of glass has been a target of scientist for more than a decade as it would permit using ordinary domestic windows to generate electricity with minimum structural alterations. Such solar cells can be used to harvest sunlight and the artificial light after sundown. One direction that is pursued is to have ultra-thin nearly transparent organic solar cells sprayed as films on a pane of glass. These windows are promoted as privacy glass.

Instead of having the entire surface as a light collecting solar cell, some windows are designed to direct the light that hits the entire surface of the window to the edges of a pane of glass where it is collected by a solar cell. One approach that has been pursued is by forming a solar concentrating organic coating on a pane of glass that absorbs non-visible electromagnetic radiation in sunlight, either ultraviolet or near-infrared, and re-emit the light at a higher wavelength, infrared, where it is transported across the pane of the window to a solar cell at the frame of the window. Alternatively, inorganic nanoparticles, quantum dots, have been co-infused in a polymethylmethacrylate (acrylic) window, where UV, violet and blue light is absorbed and undergoes a Stokes shift and emits red light that travels with nearly total internal reflectance to the edge of the window.

In another approach inorganic nanoparticle salts have been co-infused in a polycarbonate interlayer, which is then laminated between two plates of ¼″ inch glass to form a window. The nanoparticles scatter components of the electromagnetic spectrum to the edge of the glass while letting most of the spectrum through. Again, the light that reaches the edge of the glass is collected at the window frame by a solar cell imbedded therein. The transparent inorganic nanoparticles scatter incoming sunlight with most scattered light traveling laterally in the laminated structure to commercial solar cells, such as crystalline silicon cells, at the edges of the glass windows. The window remains highly transparent by proper control of the nanoparticle size and loading in the polymer. Generally, the electrical power generated by such solar windows is quite low, ˜1 W per square foot. These transparent nanoparticles scatter shorter wavelength light effectively, but do not scatter infrared light. Hence, it would be desirable to increase the harvesting of infrared light without sacrificing the transparency of the windows to the visible spectrum.

SUMMARY OF THE INVENTION

An embodiment of the invention is directed to a photovoltaic system that is a window that includes at least one combined nanoparticle polymer sheet and a frame that includes at least one photovoltaic cell to receive at least IR light directed through the window to the photovoltaic cell for the generation of electricity. The at least one combined nanoparticle polymer sheet has a transparent polymer that has at least partial transmittance in at least the visible and near IR regions of the electromagnetic spectrum. The metal nanoparticles can be imbedded within the combined nanoparticle polymer sheet or are decorated on at least one surface of the combined nanoparticle polymer sheet on surfaces parallel to the large area faces of the window. The metal nanoparticles are of sizes and shapes that have surface plasmon resonance frequencies in the near-infrared or the near-ultraviolet. The multiplicity of metal nanoparticles can have a plurality of sizes and shapes and can have a cross-section of 10 to 200 nm. The metal nanoparticles can have a core-shell structure, wherein the core is the metal and the shell is a glass or ceramic. The transparent polymer can be of one or more polymeric resins or thermoplastics, such as an acrylic, a polycarbonate, or a polyurethane. The window comprises a plurality of combined nanoparticle polymer sheets having a multiplicity of surfaces, where the surfaces are proximal and distal light receiving faces of the plurality of combined nanoparticle polymer sheets and interfaces between adjacent combined nanoparticle polymer sheets. The photovoltaic cell can be constructed with polycrystalline silicon, monocrystalline silicon, or copper indium gallium selenide. The photovoltaic system's window can have one or more glass sheets contacting combined nanoparticle polymer sheets.

Another embodiment of the invention is directed to preparing the photovoltaic system. The transparent polymer is combined with the multiplicity of nanoparticles to form at least one combined nanoparticle polymer sheet in the form of a window. The window is secured into the frame such that at least one edge of the window that is perpendicular to a light receiving face of the window contacts at least one photovoltaic cell situated in the frame such that light directed from the window perpendicular to the light receiving phase enters the photovoltaic cell. The transparent polymer can be provided as at least one solid cured resin or as a solid thermoplastic as a polymer sheet that is combined with the multiplicity of nanoparticles by decorating one or more surfaces of the polymer sheets. Alternatively, the transparent polymer can be provided as a thermoplastic melt, a polymerizable monomer mixture, or an uncured resin and combined with the multiplicity of nanoparticles by their mixing in a fluid state and solidifying the combined nanoparticle polymer sheet by cooling a melt, polymerizing a monomer, or curing a resin to lock the nanoparticles within the sheet. One or more glass sheets can be combined with the at least one combined nanoparticle polymer sheet such that glass sheets can protect the plastic and/or act as portions of a wave guide to direct the light into the photovoltaic cells.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing of a portion of a sunlight harvesting window according to an embodiment of the invention.

FIG. 2 is three light extinction spectra of gold nanoparticles with different sizes. The inset shows a SEM image of a plurality of gold nanoparticles of different shapes that can be dispersed on or within plastics for the construction of windows, according to embodiments of the invention.

FIG. 3 is the light extinction spectra of a set of gold nanoparticles with a plurality of different shapes nanospheres, nanorods, and nanoprisms, as indicated by the SEM image insets, and sizes that can be dispersed on or within plastics for the construction of windows, according to embodiments of the invention.

FIG. 4 is the light extinction spectra of a set of gold nanorods of different aspect ratio.

FIG. 5A is a cartoon of the plasmon-driven growth of Au nanoprism.

FIG. 5B illustrates the selective inhibition of facet and subsequent facet selective growth of Au nanoprism.

FIG. 6A shows the Vis-NIR spectra and TEM images of Au and silica encapsulated nanospheres.

FIG. 6B shows the Vis-NIR spectra and TEM images of Au and silica encapsulated nanorods.

FIG. 6C shows the Vis-NIR spectra and TEM images of Au and silica encapsulated triangular nanoprisms.

DETAILED DISCLOSURE

According to an embodiment of the invention, metal nanocrystals are imbedded into a transparent polymer, such as an acrylic, or decorate the surface of one or more layers of a transparent polymer, such as a polycarbonate, acrylic, or polyurethane, to selectively scatter certain portions of the solar spectrum from near-ultraviolet to visible to near-infrared, to a solar cell imbedded in the frame of a window, as illustrated in FIG. 1. The polymer may be in the form of a thermoplastic, or in the form of a cured resin. In an embodiment of the invention, the metal nanoparticles primarily scatter near-infrared and/or near-ultraviolet radiation, although the scattering of a small portion of the visible light can accompany the scattering of the near-infrared or near-ultraviolet radiation. The metal nanocrystals can be a mixture of nanocrystals of different elements or alloys and/or of different sizes and/or shapes. Due to the mixed composition, a broad portion of the near ultraviolet and/or near-infrared spectrum that enters the polymer can be directed to the edge and collected at a solar cell situated at the edge of the window at or within the window frame. In this manner, little visible light that would be transmitted through the window absent the metal nanoparticles would be lost due to the presence of the scattering metal nanoparticles. Harvesting of the near-ultraviolet and/or near-infrared light by the solar cells attached to the frame perpendicular to the face of the window can increase the electrical power output of the solar cells as the surface area from which non-visible radiation is scattered is dramatically larger than the surface of the solar cell, concentrating the radiant energy at the solar cell.

In another embodiment of the invention, the metal nanoparticles may selectively scatter portions of the visible spectrum in addition to near-ultraviolet and/or near-infrared light. The use of such nanoparticles, either by themselves or mixed together with other nanoparticles that primarily scatter near-ultraviolet and/or near-infrared light, in the same solar window structures can produce tinted windows with various colors. Furthermore, an appropriate combination of multiple types of nanoparticles that produce different color tints can yield color-neutral windows whose visible light transmittance can be adjusted by controlling the loading of the nanoparticles in the window structure.

The metal nanoparticles scatter the light at the surface plasmon resonance frequency where excitation of their surface plasmon oscillation occurs. The scattering light intensity is sensitive to the size and aggregation state of the metal nanoparticles in addition to the composition of the metal or alloy. The metals that can be used are solids, including, but not limited to, noble metals and alloys of noble metals, such as: ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, gold, rhenium, and copper. The metal nanoparticles can be formed in any manner that provides nanoparticles that are greater than about 10 nm but less than about 200 nm. The nanoparticles are of sizes and shapes that display plasmon resonance frequencies in the near infrared region or ultraviolet region of the electromagnetic spectrum. As the particles are smaller than the wavelengths of visible light and the scattered wavelengths are not of the wavelengths of visible light, the windows formed with these nanoparticles display a high light transparence and low scattering of visible light. The nanoparticles can be any shape, for example, as shown in FIG. 2. The nanoparticles can be rods or other shapes that do not have equal dimensions but where one of the cross-sections is less than 200 nm. In an embodiment of the invention, the nanoparticles are of a plurality of sizes and shapes to provide a broad spectrum of near infrared and/or ultraviolet radiation for absorption by the photovoltaic cells situated in the frame of the windows.

The plasmon resonant frequency may appear in the visible spectrum by a change in the nanoparticle shape. As shown in FIG. 3, while the gold nanoprisms show primary plasmon resonant frequencies in the infrared region, the nanorods have primary plasmon resonant frequencies at wavelength range of about 640 nm to 720 nm. Moreover, the nanospheres show resonant peaks in both the visible (about 530 nm) and infrared (about 800 to 900 nm) regions.

Each type of these nanoparticles can be used to produce a specific tint because of their different spectral response. An appropriate combination of multiple types of nanoparticles can then produce color-neutral windows that have mostly constant transmittance throughout the visible spectrum. Certainly, all these visible-scattering nanoparticles can be combined with others that primarily scatter near-infrared and/or near-ultraviolet light to enhance the overall light harvesting efficiency.

In an embodiment of the invention, the metal nanoparticles are dispersed as filler in a plastic or resin continuous matrix that is a layer that defines the surface area of the window. In another embodiment of the invention, the nanoparticles are dispersed on at least one face of at least one plastic or resin layer within the window. The window may be of a laminate structure where a plurality of layers includes at least one plastic or resin layer. The plastics are advantageous in that they provide transparency, structure, impact resistance, and thermal insulation. The windows can be thicker than a typical single-strength glass of 3/32″, or double-strength glass of ⅛″, or even plate glass of 3/16″. The plastic can be the laminate between multiple layers of glass, for example, the multiple layers of a glass bullet-resistant pane. The plastic can be a layer of more than one inch in thickness. The polymer is one that does not absorb significantly in the near-infrared, below about 1200 nm in wavelength, such as an acrylic resin or a polycarbonate sheet.

The metal nanoparticles are dispersed in the plastic or resin matrix such that there are few aggregates of the metal nanoparticles in or on the polymer layer; for example, the fraction of metal nanoparticles in contact with another metal nanoparticle is 0.1 or less. The metal nanoparticles can be dispersed in a melt or solution, or dispersed in a monomer mixture that includes an initiator upon solidification of the mixture. For example, an acrylate resin, which is primarily methylmethacrylate with other monomers, including cross-linking monomers, initiators, and fillers, can be use in a neat liquid phase where the metal nanoparticles are dispersed into the monomer mixture with high-sheer mixing and where the monomer mixture polymerized to the solid window sheet with little agglomeration of the metal nanoparticles before the mixture is sufficiently viscous to discourage diffusion and agglomeration within the composite. In like fashion a polycarbonate can be taken up in a solvent and the particles dispersed followed by removal of the solvent, or, alternatively, by the polymerization of melted cyclic carbonate oligomers with dispersed metal nanoparticles to prepare the polymer layer of the window.

The use of glass sheets, or other low oxygen diffusion sheets, on the faces of the window, as shown in FIG. 1, permit functioning as a wave guide where internal reflection directs the scattered near-infrared light through the window perpendicular to the light entry surface to a solar cell within the frame of the window. The window frame contains one or more solar cells that can collect the scattered near-infrared light from the metal nanoparticles. The solar cells can be any type of solar cell that absorbs sufficiently in the near-infrared, including, but not limited to: polycrystalline silicon, monocrystalline silicon, or copper indium gallium selenide. In addition to Cu(InGa)Se₂ (CIGS), other direct bandgap materials with low gaps can be used for the solar cells in the window frames. Other photovoltaic cells, including polymeric and dye sensitized cells, can be designed to extend the absorption of radiant energy further into the ultraviolet and/or infrared regions of the electromagnetic spectrum and can be employed in the window based photovoltaic system. The exterior faces of the window can be a polymer of like or dissimilar composition as the polymer with the decorated or infused metal nanoparticles. The frame can be constructed of a plurality of solar cells combined as an array.

In embodiments of the invention, windows with high visible light transmission (VLT) contain only IR-scattering nanoparticles. In other embodiments of the invention, photovoltaic windows having blue, green, or brown hues are formed by inclusion of visible and IR scattering nanoparticles into the films on the windows. These windows can include pigments and other components that additionally or exclusively provide the colors of the tinted windows. In another embodiment of the invention, multiple types of visible-scattering nanoparticles can be combined to achieve low VLT/non-tinted photovoltaic windows or low VLT tinted windows with the additional inclusion of pigments.

Efficient scattering of visible and NIR light is required to achieve solar windows where the VLT ranges from low to high. The light-harvesting nanoparticles included in the window must be capable of scattering across a broad range of the solar spectrum. The surface plasmon resonance (SPR) of plasmonic metal NPs can be tuned to maximize the scattering of incident light over a broad range by manipulating their sizes and shapes. Selective use of nanorods or nanoprisms allows alteration of the SPR modes of the nanoparticles across the entire visible and NIR regions of the solar spectrum, as shown in FIG. 3. Plasmonic nanospheres (˜400-550 nm), nanorods (˜500-900 nm), and nanoprisms (˜800-1400 nm) can be used to promote scattering across the broad range of 400 to 1400 nm. It is also noted that those solution-based methods employed herein can be easily extended for large-scale nanomaterials synthesis.

In embodiments of the invention, Au nanoparticle of differing morphologies can be used, according to embodiments of the invention. Small Au seed nanoparticles (d≈4-6 nm) can be prepared by NaBH₄ reduction of HAuCl₄, and can be used for subsequent growth in aqueous solution. Such aqueous solutions contain capping agents, including, but not limited to, cetyltrimethylammonium bromide (CTABr)), and HAuCl₄·3H₂O, and reducing agents, such as, but not limited to, ascorbic acid, with base solution employed to adjust pH. By varying solution temperature, pH, and HAuCl₄ concentration, various Au nanoparticles can be produced.

In other embodiments of the invention, the optical properties of the colloids can be tuned by the use of plasmonic alloys, such as, but not limited to, Au/Ag alloy or by use of core-shell nanoparticles, such as, but not limited to, Au-Ag core-shell nanoparticles. Such particles can be formed by the simultaneous or sequential reduction of, for example, HAuCl₄ and AgNO₃ salts. The LSPR of Au nanoprisms occurs around 1200 nm, but formation of a glass shells on a Au nanoprism induces a significant blue-shift in the LSPR maximum to about 1000 nm.

In an embodiment of the invention, Au nanorods can be used as “seeds” for the subsequent growth of anisotropic Au nanorods and/or nanowires. The length of the Au nanorods can be tuned by changing the concentration of the capping reagent, such as CTABr, and the ratio of the Au seeds to the HAuCl₄ precursors in the growth solution. The plasmon bands of the Au nanorods can be chosen from ˜550-900 nm and can be combined to extend the absorption across any portion of the visible and near-IR spectrum, as shown in FIG. 4. Interestingly, our initial results revealed that the Au nanoparticle morphology can be easily tuned by simply varying the iodide (I) concentration in the growth solution. Bu controlling the amount of iodide in the solution, a large population of nanorods can be obtained when no I⁻ is in solution or a large population of nanoprisms at concentration of I⁻ greater than 10 with the shapes and scattering shown in FIG. 2. By further adjusting the I⁻ concentration, tip truncation of the nanoprisms can be controlled to alter the LSPR properties. For instance, the LSPR of the nanoprisms can be tuned from 1000-1200 nm by changing the I⁻ concentration from 50-500 μM NaI in the growth solution. The nanorod or nanoprism aspect ratio can be tuned by adjusting the ratio of seed particles to metal precursors in the growth solution.

Light-mediated synthesis of metal nanocrystals allows synthesis of nanostructures with precise control over morphology. In this manner, Ag nanoprisms have been prepared that have strong absorption in the NIR region, where the architecture of the nanoprisms correlates in a quasi-linear fashion with the in-plane dipole plasmon band. When the light has a wavelength that matches the SPR bands of the plasmonic seed nanoparticles in the solution, nanoparticle growth is initiated. The SPR bands of the growing nanoparticles red-shifts as their sizes and shapes change. Once the SPR bands shift from that of the light source, nanoparticle growth stops. By adjustment of the illumination to match the new SPR bands, growth of the nanoparticle can be continued in a controlled manner. By this method, Au nanoprisms with strong SPR absorption in the NIR region can be prepared. Using sharp band-pass filters for narrow wavelength distribution or by use of lasers as the light source, Ag nanoparticles with uniform size and shape can be acquired in high yield.

Pseudo-spherical Au nanoparticles with an average size of ca. 7±3 nm are useful as seeds for plasmon-driven growth of anisotropic Au nanoprisms. Photochemical growth solution can be prepared by adding polyvinylpyrrolidone (PVP) to pure H₂O and methanol to which HAuCl₄ aqueous solution and Au seed solution are added and gently mixed. As illustrated in FIG. 5A, for high yield synthesis of Au nanoprism, growth solution is first incubated in the dark to preferentially enlarge multiply-twinned seeds while rendering planar-twinned seeds relatively unreactive in the dark. The multiply-twinned nanoparticles are large enough (d>100 nm) to be readily separated from the planar-twinned seeds (d˜15 nm) by centrifugation. The supernatant of highly enriched with planar-twinned nanocrystals is irradiated at an incident power I₀ of about 12 mW/cm² to produce Au nanoprisms in high yield. The facets along the nanoprism perimeter is alternatively enclosed by { 111} and {100} facets. If a facet-selective species such as iodide is in the growth solution, preferential passivation of { 111} facets occurs with growth occurring on the {100} facets to yield triangular nanoprisms as the dominant photoproducts, as indicated in FIG. 5B.

The optical properties of plasmonic nanoparticles are highly sensitive to their physical morphology and, therefore, it is essential to preserve the geometry of the nanoparticles to ensure consistent operation over time. In an embodiment of the invention, glass or ceramic shells, for example, silica (SiO₂) shells, coat plasmonic metal nanoparticles (Au, Ag, etc.). These core-shell nanoparticles are used to provide plasmonic material with enhanced chemical stability due to the silica physical barrier between the metal and its environment. After the desired nanoparticles are synthesized, coating with SiO₂ shells results by injecting small quantities of tetraethoxysilane (TEOS) to form silica on the nanoparticles source. By adjusting the amount of TEOS and the number of its additions to the growth solution, the thickness of the SiO₂ shell can be tuned from about 5 to 25 nm. These conformal coatings preserve the optical response of the metal nanoparticle colloid, as illustrated for various morphologies of Au and Au-silica core-shell nanoparticles in FIGS. 6A, 6B and 6C. In addition to SiO₂, the glass or ceramic shell can be another metal oxide, including, but not limited to TiO₂, Al₂O₃, SnO, Al₂O₃, B₂O₃, ZrO₂, SnO₂, any combination thereof, or any other metal oxide.

In the first method, the properly functionalized nanoparticles may be mixed with the PMMA monomers. The organic-inorganic composite material will then be spread out on a glass plate followed by the pressing of the second plate on top. For commercial production, it is conceivable to injection mold the PMMA/metal nanoparticle composite material into thin sheets, which are then laminated between two glass plates to produce the desired waveguide. This mixing method can easily adjust the loading of the nanoparticles, and with variable PMMA layer thickness, the amount of nanoparticles within the waveguide and therefore the optical transmittance can be readily tuned. However, it may be difficult to control the orientation of the anisotropic particles, which could prove critical for achieving high solar conversion efficiencies in the photovoltaic windows.

To control orientation of the anisotropic nanoparticle, such as nanoprisms and nanoplates, direct deposition onto one glass plate using solution processes such as spin coating or spray coating can be carried out. If desired or required, glass surface may need to be pretreated in oxygen plasma to improve wetting of the nanoparticle containing solution on the surface. For Example, Norland Optical Adhesive (NOA) precursors can be spread on a second glass plate, which is then pressed against the nanoparticle-coated surface of the first glass plate. The waveguide is completed by curing the NOA under UV irradiation. Multiple coatings of the nanoparticles can be formed, for example, by depositing a layer of nanoparticles on the first glass plate, spraying dissolved NOA, for example in toluene, onto the nanoparticles and rapidly drying and UV-polymerizing the NOA. Subsequently, repeated depositions of additional nanoparticles and polymerized NOA layers allow a host of non-aggregable metal nanoparticles. The number of coating cycles and the concentration and solution deposition conditions can be varied to control the amount of the plasmonic nanoparticles within the waveguide. Photovoltaic windows are constructed by attaching commercially available solar cells to the edges of the waveguide using optical adhesives.

It should be understood that the embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application. 

We claim:
 1. A photovoltaic system, comprising: a window comprising: a combined nanoparticle polymer sheet, the combined nanoparticle polymer sheet comprising a transparent polymer and a multiplicity of metal nanoparticles, the transparent polymer having transmittance in visible and near-infrared regions of an electromagnetic spectrum, wherein the metal nanoparticles are imbedded in the combined nanoparticle polymer sheet; and a first glass sheet and a second glass sheet, the combined nanoparticle polymer sheet sandwiched between and in contact with the first and second glass sheets to produce a waveguide; a frame comprising at least one photovoltaic cell configured to harvest from the near-infrared and/or the near-ultraviolet regions of the electromagnetic spectrum, the at least one photovoltaic cell residing in the frame perpendicular to a light receiving face of the window; and wherein a portion of the near ultraviolet and/or a portion of the near-infrared spectrum that enters the combined nanoparticle polymer sheet is directed to an edge of the waveguide to be received by the at least one photovoltaic cell, wherein the multiplicity of metal nanoparticles are of a plurality of sizes and shapes, wherein a majority of the metal nanoparticles are isolated from each other, wherein a fraction of the metal nanoparticles in contact is 0.1 or less, wherein the multiplicity of metal nanoparticles have a cross-section of 10 to 200 nm, wherein the metal nanoparticles comprise a metal selected from ruthenium, rhodium, palladium, osmium, iridium, platinum, rhenium, gold, silver, and copper, and alloys thereof, and wherein the metal nanoparticles are configured to scatter selected regions of the electromagnetic spectrum to the frame, and the metal nanoparticles are of sizes and shapes that have a peak surface plasmon resonance frequency in the near-infrared to the near-ultraviolet regions of an electromagnetic spectrum.
 2. The photovoltaic system according to claim 1, wherein the metal nanoparticles comprise a core-shell structure, and wherein the core comprises the metal and the shell is a glass or ceramic.
 3. The photovoltaic system according to claim 2, wherein the glass or ceramic comprises, SiO₂, TiO₂, Al₂O₃, SnO₂, ZrO₂, or any combination thereof.
 4. The photovoltaic system according to claim 1, wherein the transparent polymer comprises one or more polymeric resins or thermoplastics.
 5. The photovoltaic system according to claim 4, wherein the polymeric resin or thermoplastic comprises an acrylic, a polycarbonate, or a polyurethane.
 6. The photovoltaic system according to claim 1, wherein the window comprises a plurality of combined nanoparticle polymer sheets having a multiplicity of surfaces wherein the surfaces are proximal and distal light receiving faces of the plurality of combined nanoparticle polymer sheet and interfaces between adjacent combined nanoparticle polymer sheets.
 7. The photovoltaic system according to claim 1, wherein the photovoltaic cell comprises polycrystalline silicon, monocrystalline silicon, or copper indium gallium selenide.
 8. The photovoltaic system according to claim 1, wherein the multiplicity of metal nanoparticles are spheres, rods, prisms, disks, rice-shaped, shelled, donut-shaped, or any combination thereof.
 9. The photovoltaic system according to claim 1, wherein the multiplicity of metal nanoparticles imparts a tint, a color-neutrality, or a variable light transmittance in the visible spectrum over portions of the window.
 10. The photovoltaic system according to claim 1, wherein the combined nanoparticle polymer sheet is formed by mixing the transparent polymer in a fluid state with the multiplicity of nanoparticles and solidifying to form the combined nanoparticle polymer sheet.
 11. The photovoltaic system according to claim 1, wherein in addition to the portion of the near-infrared spectrum, at least one of a portion of the near ultraviolet spectrum and a portion of the visible spectrum that enters the combined nanoparticle polymer sheet is directed to an edge of the waveguide to be received by the at least one photovoltaic cell. 